This application is based on and incorporates herein by reference Japanese Patent Application No. 2003-24610 filed on Jan. 31, 2003.
The present invention relates to an in-vehicle radar system mounted in a vehicle capable of accurately estimating a width center of a preceding vehicle even when the preceding vehicle is moving in an adjacent lane.
A scan-type radar mounted in a reference vehicle radiates transmission radio waves around the reference vehicle to detect an object based on reflected radio waves within a given region ahead of the reference vehicle. U.S. 5,745,070 discloses an in-vehicle scan-type radar system that determines whether a preceding vehicle exists in a lane in which a reference vehicle equipped with the scan-type radar is moving while the reference vehicle is moving around a curve. Here, while the reference vehicle is moving around the curve, the scan-type radar operates as follows: to estimate an existing orientation of a central position of the object based on a curving radius of the curve and a relative distance to the object; to set a vehicle moving lane area that extends with a given angle on either sides of the existing orientation; and to modify so that an inward area of the vehicle moving lane area located on an inward side of the curve with respect to the existing orientation is increased more than an outward area of the vehicle moving lane area.
Thereby, even when the central position of the object is detected as being biased to the inward area while the reference vehicle is moving around the curve, the existing orientation of the center position of the object is corrected outwardly in the vehicle moving lane area. This results in properly determining whether the object exists in the lane in which the reference vehicle is moving.
In the above radar system, the existing orientation of the center position of the object is estimated by the following reasons. Namely, when a reference vehicle is moving around a curve, a backside of a preceding vehicle does not face in front of the reference vehicle. Here, the transmission radio waves from the reference vehicle are radiated upon, of the object, the backside, the inner side that faces an inward portion of the curve, and a corner between the backside and the inner side. The transmission radio waves radiated upon the backside and the inner side are reflected towards a direction different from a direction where the reference vehicle is located, while the transmission radio waves radiated upon the corner are largely reflected to the direction where the reference vehicle is located. When receiving the radio waves reflected from the corner, the radar system detects the reflected radio waves as a reflection object having a width whose width center is biased to the corner that is located in an inward side of the curve from the actual center.
Thus, while the reference vehicle is moving around a curve, a data center of the detected width of the reflection object does not correspond to the actual width center of the object. The central position of the object is therefore estimated based on the curving radius of the curve and the distance to the object.
However, a case where the data center of the reflection object does not correspond to the actual width center of the object is not limited to a case where the reference vehicle is moving around the curve. For instance, suppose that in a straight road shown in FIG. 11, a preceding vehicle 30 is moving in a lane adjacent to a lane in which a reference vehicle 20 is moving. Here, the transmission radio waves from the reference vehicle 20 are radiated upon not only the backside of the preceding vehicle 30, but also the side and corner of the preceding vehicle 30. A data center of the preceding vehicle 30 is biased from the actual width center of the preceding vehicle 30.
The conventional estimating method is used for a case where a preceding vehicle 30 is moving in the same lane in which the reference vehicle 20 is moving. It is therefore not used for the above case where a preceding vehicle 30 is moving in a lane adjacent to a lane in which the reference vehicle 20 is moving.
An object of the present invention is to provide an invehicle radar system mounted in a reference vehicle cap able of properly estimating a width center of a preceding vehicle even when the preceding vehicle is moving in a lane adjacent to a lane in which the reference vehicle is moving.
To achieve the above and other objects, an in-vehicle radar system mounted in a reference vehicle is provided with the following. Transmission radio waves are radiated and reflection radio waves are detected from a reflection object that receives a portion of the transmission radio wave s. A distance to the reflection object and an orientation of the reflection object with respect to the reference vehicle are recognized based on the detected reflection radio waves from the reflection object. A relative position of a width center of the reflection object with respect to the reference vehicle is computed based on the recognized distance and the recognized orientation. A curving radius of the road is detected. A relative rotation angle of the reflection object that is an angle between a direction of the transmission radio waves advancing to the width center of the reflection object and a direction perpendicular to the width direction of the reflection object is computed based on the computed relative position and the detected curving radius. The computed relative position of the width center of the reflection object is corrected by using the computed relative rotation angle.
For instance, in a straight road, when transmission radio waves are radiated to a preceding vehicle moving in an adjacent lane, the transmission radio waves are radiated on, of the preceding vehicle, a backside, a side, and a corner between the backside and the corner. Here, the reflection radio waves are mainly from the corner of the preceding vehicle to the reference vehicle. The radar system recognizes that an orientation of the reflection object is a direction of the maximum reflection strength of the reflection radio waves. A width center of the preceding vehicle is thereby estimated as being located around the corner of the preceding vehicle. The estimated width center does not correspond to an actual width center of the preceding vehicle, so that a lateral bias is generated.
To correct the lateral bias, for instance, a lateral bias correction amount is previously obtained according to a relative rotation angle. The lateral bias correction amount according to the computed relative rotation angle is used for correcting the lateral bias of the computed relative position of the width center. As a result, in the structure of the radar system of the present invention, a width center of a preceding vehicle moving in an adjacent lane can be accurately estimated.